IQ 178

A 178 is 18 points past the ceiling most major tests publish. The model rarity, about 1 in 10 million, describes about 810 people worldwide, which is far beyond anything a test has been checked against.

No test has enough people in its norm sample to check its accuracy at 178. In a 2,200-person sample the bell curve expects effectively nobody at 178 or higher.

Real populations may not follow the bell curve perfectly in the far tails, so rarity figures this extreme are illustrations, not head counts.

A 178 almost never comes from a modern, supervised adult test. It usually comes from somewhere like this:

• Different scales. Some tests use a standard deviation of 24, so a 178 there is about 149 on the usual SD 15 scale.
• Unnormed online quizzes. A test with no norm data can print any number. Very high outputs usually say more about the scoring than the person.
• Repetition without a source. Numbers attached to celebrities are often copied from site to site with no test report behind them.

42 of the historical profiles on this site carry an estimate of 160 or more, and 4 reach 178 or higher. Isaac Newton and Leonardo da Vinci are the classic examples. Their numbers are retrospective judgements based on their work, not test scores.

Two people with identical estimates can have very different evidence behind them. Each profile explains what its estimate is based on and how confident anyone can be.

If IQ follows the standard bell curve, 0.00001% of people score 178 or higher. Here is what that share means across whole populations:

An IQ of 178 or higher is 5.7 times rarer than 173 or higher, and 183 or higher is 6.3 times rarer again. At this point on the curve, each extra point makes a score about 43% rarer.

What your 178 could really be. Even a good supervised test has a margin of error of roughly 5 points either side, and far more at this height. A true score from 173 to 183 would span rarities from 1 in 1.8 million to 1 in 63 million.

Which scale was it on? A 178 reported on an SD 16 scale converts to about 173 on the usual SD 15 scale, and one from an SD 24 scale (seen in some Cattell-style results) to about 149. Check which scale your score report used.

Nobody famous has a verified IQ in most cases, and retrospective estimates are only made for a narrow group.

No historical figure on this site has an estimate close to 178. Retrospective estimates cluster between about 115 and 250 because they are only made for people with exceptional achievements. That is a selection effect, not a sign that famous or successful people cannot score 178.

Nearby scores and the round-number landmarks, so you can see how quickly the percentile changes around 178. Every row links to that score's page.